I was lucky enough to find a Rab Microlight Alpine jacket in a small on a rack at my local REI.
Since they don't carry it in the store, presumably, someone bought it online (with free shipping, since it was over $50), and returned it locally to the store (for free).
I got lucky and got to try it on!
The small fit perfectly, was cozy and seemed like a quality jacket. Unfortunately, the hood was so short it seemed like it was made for someone with no neck :) When I put the hood up, I had to pull it up over my head and the jacket actually raised up and inch or so, making the entire weight of the jacket pull down from the top of my head. It was almost comical! I have read such good things about this jacket, so I wonder if it is actually a manufacturing error since the hood was so grossly mis-sized. (I am a very average size and easily fit into a small or medium for almost any brand.)
Rab is out, despite the hood issue. Even if it was a defective coat, just putting it on at REI made me realize that I don't want a down jacket that is almost 1 lb for a summer thru hike, even if it's in the mountains. That is just too much weight to carry for the few nights of frost, and extra warmth assurance. Too bad–it's on Steep and Cheap right now.
I'd like to try a few Mont Bell down jackets, but they just don't exist around here.
For now, I am going with a Uniqlo Women's Ultra Light Down jacket (90% down). http://www.uniqlo.com/us/product/women-ultra-light-down-jacket-133103.html for about $60 / 5-7 ounces, and I am thrilled. It seems to be only sold in their own stores or on their own website, so if I order I'm gonna have to pay for shipping on this one because it's too cheap for free shipping! Or increase my sales total by ordering both a Small and Medium (to be sure of my size) and pay for return shipping for the one that doesn't work. Either way, I need pay a couple bucks for shipping. But for a $60, supposedly decent jacket, I don't mind so much on principle :) More likely, I'll be able to pass through one of their stores before my trip and try a few on in person.